The present invention relates to sleep monitoring methods, in particular methods for identifying breathing parameters that are characteristic to the breathing status of a sleeping individual, methods of controlling breathing apparatuses, and methods of signalizing the breathing status in sleeping individuals. The present invention also relates to devices for implementing said methods, in particular, monitoring devices, breathing apparatuses, pressure generators, and control devices therefor. In addition, the present invention also relates to methods for the detection and treatment of sleep-disordered breathing and devices for implementing said methods.
Sleep-disordered breathing is a widespread disease which can manifest itself in various forms. In many cases, obstructive sleep apnea (OSA) with daytime sleepiness and associated cardiovascular diseases is involved (see, e.g., P. J. Strollo Jr. et al. in N. Engl. J. Med., vol. 334, 1996, page 99). As a result of an increased upper airway resistance (UAR), the upper airways recurrently collapse in the sleeping individual who is suffering from this disease. Even if the obstruction of the upper airways is not complete, increased UAR will still cause clinical symptoms.
Presently, the diagnosis of obstructive sleep apnea involves screening which is able to detect apnea relatively reliably but does not detect so-called hypopnea (breath with reduced flow) with a comparable level of reliability. Measurements of oxygen saturation and of the respiratory flow measured on mouth and nose are carried out. These diagnostic procedures are generally used when a patient complains of daytime sleepiness. But daytime sleepiness is also seen in individuals who experience many interruptions of their sleep (so-called micro-arousals) which occur in the presence of the UAR syndrome (UARS) because the upper airways are narrow without being completely obstructed. The organism must exert considerable pressure to maintain the respiratory flow. Large variations in the pressure in the chest are presumably the cause of micro-arousals and may be responsible for subsequent negative effects on the cardiovascular system. Conventional diagnostic procedures are not able to identify this problem since, due to the high pressure exerted, the respiratory flow is not reduced to a significant extent. The only way to measure the pressure would be to use an intraesophageal balloon which would involve an invasive procedure and cause considerable discomfort to the patient.
The conventional way to detect UARS has been to measure the esophageal pressure and, at the same time, detect micro-arousals (see, e.g., C. Guilleminault et al. in Chest, vol. 104, 1993, page 78 1). But these procedures require a high degree of technical complexity, they are time-consuming and invasive, and they cause the patient discomfort.
It is also known that an increased UAR is associated with changes in the measurable respiration variables of state, e.g., the pressure contour (see J.-J. Hosselet et al. in Am. J. Respir. Crit. Care Med., vol. 157, 1998, page 1461) or the breath cycle lengths (see, e.g., T. Brack et al. in Am. J. Respir. Crit. Care Med., vol. 157, 1998, page 1756). So far, however, this insight has not yet been translated into sleep monitoring applications.
Until now, patients with sleep-disordered breathing problems have been treated with so-called CPAP therapy (CPAP=continuous positive airway pressure). In the treatment with CPAP, the sleeping patient receives continuous positive airway pressure treatment via a nasal mask that is connected to a breathing apparatus (CPAP apparatus).
The disadvantage of CPAP therapy is that the patient is exposed to positive airway pressure over the entire duration of his or her sleep, i.e., for the entire night. This subjects the patient to considerable stress. To reduce this stress as much as possible, a conventional CPAP apparatus is operated at the lowest possible pressure. This, however, entails a risk. In some cases, the operating pressure of the CPAP apparatus may be too low.
Thus, the problem to be solved by the present invention is to make available an improved method of identifying breathing parameters in a sleeping subject, said method is marked especially by the measurement of the simplest possible signal while subjecting the patient to the least stress possible and by expanded applicability, such as is involved in the control of breathing apparatus or in signaling breathing disturbances. Another problem to be solved by the present invention is to provide devices for implementing and using said methods.
These problems are solved by a method, a computer program, or devices having the features described in claims 1, 6, 8, 10, 12, and 13. Useful embodiments and applications of the invention result from the dependent claims.
The basic objective of the present invention is to make available a method of identifying breathing parameters that are characteristic for the breathing status of a sleeping individual, with which method the derivative function with respect to time of at least one variable of status of the cardiovascular system of the patient, which variable undergoes recurrent changes while the patient is breathing, is measured and subjected to a rhythm analysis so as to identify, as breathing parameters, the statistical values of distribution of breath-to-breath intervals in the unobstructed breathing phases or variables derived therefrom (variables which are calculated from the statistical values of the distribution of the breath-to-breath intervals). The breathing parameters to be identified are, e.g., the variability or the so-called kurtosis value of the breath-to-breath intervals under consideration. Any physical or chemical property of the individual that changes parallel in time with the rhythm of the recurrent inspiration and expiration of the individual can be measured as a variable of state of the cardiovascular system. Thus, for example, the flow of air during respiration or the hearth rhythm can be measured. The rhythm analysis of one single variable of state that correlates with the breathing and the statistical analysis of the variability over time of the variable of state in time intervals in which a physiologically normal breathing pattern is present has the advantage that a simple one-channel signal is analyzed by means of which characteristic sleep stages of the individual can be extremely reliably identified.
According to a preferred embodiment of the present invention, a minimum of one of the breathing parameters identified is used to control a breathing apparatus, in particular a pressure generator of a breathing apparatus. Surprisingly, the inventors discovered that the breathing parameters identified according to the present invention are suitable for controlling the operating status of breathing apparatuses, in particular with regard to the level of the auxiliary pressure to which the patient is subjected, e.g., to avoid OSA or UAR syndromes. Thus, the subject matter of the present invention concerns especially a control procedure for breathing apparatuses, with which procedure a pressure generator of the breathing apparatus is controlled as a function of the breathing parameters and the value of the generated pressure is set. This control procedure has the advantage that the substantially known CPAP treatment can be carried out in a less stressful manner by increasing the pressure only when a dangerous breathing situation arises. As a result, the discomfort for the patient is considerably reduced.
According to another preferred embodiment of this invention, a minimum of one of the breathing parameters is used to control a sleep monitoring apparatus which is designed to signal and/or register breathing disturbances. It was discovered that by comparing the breathing parameters identified according to the present invention to reference values of healthy individuals, these parameters can be suitably used for supplying reliable data on the intermittent obstruction or occlusion of the upper airways of a sleeping individual. Thus, the subject matter of the present invention also concerns a method of signaling and/or registering interruptions of sleep caused by breathing disturbances. Preferably, signaling is done with visual signals (LED display or screen display, logging printer) or acoustic signals (alarm).
Another subject matter of the present invention concerns the method of the above-mentioned rhythm analysis of measured variables of state of the cardiovascular system of an individual, which recurrently change over time in correlation with the respiration and, in particular, computer programs tools for implementing such methods.
Devices according to the present invention for implementing the methods mentioned above include, in particular, breathing apparatuses with controllable pressure generators and sleep monitoring devices with signaling devices that are chosen on the basis of the specific application. The sleep monitoring device as such can be part of the breathing apparatus. The pressure generator and/or the signaling device is/are operated as a function of the breathing parameters identified according to the present invention and predetermined reference values. The breathing apparatus forms a feedback control circuit in which the variable of state of the cardiovascular system is continuously measured, analyzed, and compared to the reference values. The pressure generator is set as a function of the result of the comparison to the reference values. Accordingly, a device according to the present invention comprises a measuring device, a processor circuit, and an actuating device for the pressure generator.
This invention has the following advantages. The breathing parameters identified according to the present invention make it possible monitor sleep reliably and reproducibly. Simple signal processing is provided. The stress on the individual caused by the measured data acquisition is low. Breathing and/or sleep monitoring apparatuses can be designed for use in a clinical environment (sleep laboratory) or for personal use by individuals. The invention can be universally implemented for use on any patient, in particular regardless of the age of the patient. According to the present invention, a simple and easy method is provided which makes it possible to detect the UAR symptom. In the presence of symptoms which are similar to those suffered by patients with OSA, conventional means could detect an UAR symptom only by means of complicated measurements of the esophageal pressure, something that is avoided when the method according to the present invention is used.